Adjustable shunt core



May 9, 1967 Filed Sept. 1, 1965 H. F. WEARLEY ADJUSTABLE SHUNT CORE 2 Sheets-Sheet 1 1040 V01 D965 RANGE SHAME? I MPG mnanp --7 Ai I Y A 1 I A s fan/ente sum/002v COEE-NFMA. w rjn ADJUSTABLE SHUNT CORE Filed Sept. 1, 1965 2 Sheets-Sheet 2 [27 1/827 for. Homer FT Mar/4.19,

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United States Patent 3,319,204 ADJUSTABLE SHUNT CORE Homer F. Wearley, Payne, Ohio, assignor to General Electric Company, a corporation of New York Filed Sept. 1, 1965, Ser. No. 484,201 1 Claim. (Cl. 336-134) The invention relates to an adjustable shunt core, and particularly to an adjustable shunt core for a leakage or high reactance transformer.

A leakage or high reactance transformer utilizes a shunt magnetic path positioned between the primary Winding and the secondary winding of the transformer. This shunt path usually comprises a magnetic material (such as iron) and air. This shunt path limits the currents in the secondary winding of the transformer. Formerly in the manufacture of leakage or high reactance transformers, the shunt paths were provided by the insertion of a precalculated amount of magnetic material between the primary and secondary windings of each transformer. However, because of the needed manufacturing tolerances, it was difficult to produce such transformers with identical or similar characteristics, particularly the magnitude to which the current in the secondary winding is limited. This was especially true if the transformer was formed of laminations. If the inserted shunt path for a given transformer did not provide the desired limited magnitude of secondary current, the addition or removal of a lamination usually decreased or increased this secondary current an excessive amount. Such a situation made massproduction of such transformers difficult and expensive. And if the magnitude (to which the secondary current was to be limited) had to be held to a close tolerance, mass-production of such transformers was even more difficult and expensive.

Accordingly, an object of the invention is to provide an improved leakage or high reactance transformer.

Another object of the invention is to provide a leakage or high reactance transformer that is relatively easy to manufacture within relatively close tolerances of operating characteristics.

Another object of the invention is to provide an improved leakage or high reactance transformer that is relatively easy to assemble, and that is relatively easy to adjust after assembly so that the secondary current of the transformer is limited to a predetermined magnitude.

Briefly, these and other objects are attained in accord ance with the invention by a core structure having a modified E-shaped portion and a modified I-shaped portion. These portions may be formed of laminations if desired. The two portions are dimensioned so that when they are assembled, the center leg of the E-shaped portion and the projection of the I-shaped portion are adjacent. The center leg and the projection are sloped and parallel at their facing surfaces. The air gap between these facing surfaces can be varied by rnovin g the modified E-shaped portion and the modified I-shaped portion relative to each other. The transformer with the primary and secondary windings can be assembled and then the modified E-shaped portion and the modified I-shaped portion can be moved so as to provide the air gap that results in the secondary current being limited to the desired magnitude.

The invention may be better understood from the following description given in connection with the accompanying drawing, and the scope of the invention is pointed out in the claim. In the drawing:

FIGURE 1 shows a front elevational view of a leakage or high reactance transformer utilizing the adjustable shunt core of the invention;

FIGURE 2 shows a top view of the transformer of FIGURE 1;

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FIGURES 3a and 312 show the adjustable shunt cores only of FIGURES 1 and 2 in two extreme positions of adjustment; and

FIGURE 4 shows curves illustrating how the shunt core of the invention can be adjusted to provide a secondary currgnt that is limited to the desired predetermined magnltu e.

FIGURES 1 and 2 show a leakage or high reactance transformer utilizing the adjustable shunt core in accordance with the invention. This transformer comp-rises a modified I-shaped portion 10 and a modified E-shaped portion 12. These portions 10, 12 may be formed of suitable solid magnetic material or, as is generally preferred, may be formed of laminations of suitable magnetic material. The I-shaped portion 10 comprises a horizontal or longitudinal portion with a triangularly shaped projection 14 at a suitable location between the ends of the longitudinal portion. The E-shaped portion 12 includes outer legs 16, 18 and a center or inner leg 20. The portions 10, 12 are designed so that the projection 14 on the I-shaped portion 10 and the center leg 20 on the E- shaped portion 12 are at corresponding positions with their facing surfaces sloping at approximately or substantially the same angle relative to the long axis or dimension of the transformer. The modified I-shaped portion 10 has flat surfaces at its ends which engage or ride on respective surfaces of the outer legs 16, 18 so that the modified I-shaped portion 10 and the modified E-shaped portion 12 can be moved longitudinally with respect to each other. In accordance with the invention, this longitudinal movement permits the air .gap between the facing surfaces of the projection 14 and the center leg 20 to be adjusted. The transformer also comprises a primary winding 22 positioned around the I-shaped portion 10 and between the legs 16, 20 of the E-shaped portion 12; and a secondary winding 24 positioned around the I-shaped por tion 10 and between the legs 18, 20 of the E-shaped portion 12. Insulation 23 was provided for the primary winding 22, and insulation 25 was provided for the secondary winding 24.

In the construction of a transformer such as shown in FIGURES 1 and 2., the modified l-shaped portion 10 and the modified E-shaped portion 12 were respectively formed by stacking a suitable number of laminations. Then, the windings 22, 24 (previously wound, wrapped, and taped to hold their shape) were placed over the -I- shaped portion 10. The insulation '23, 25 was added, and the modified E-shaped portion 12 was placed in position with the outer legs 16, 18 facing or butting against the I-shaped portion 10. The two portions 10', 12 were clamped together by conventional friction clamps 26 placed over the ends of the assembled portions 10*, 12. As shown in FIGURE 1, the portions 10, 12 had suitable indentations or notches at their ends to provide a better friction surface for the clamps 26. The clamps 26 were designed and dimensioned so that they held the two assembled portions 10, 12 in fixed relation with respect to each other, but so that the portions 10', 12 could be moved longitudinally and adjusted with respect to each other by the application of suitable force. This adjustment can be made with the transformer in a suitable jig with the modified E-shaped portion 10 held against movement by a projection of the jig fitting into a notch 30*. A suitable lever attached to the jig engages a notch 28. Movement of this lever moves the I-shaped portion 10 longitudinally (-i.e., left and right as viewed in FIG- URE l) with respect to the E-shaped portion 10. After adjustment of the transformer has been completed, the transformer may be coated with a suitable material such as asphalt or varnish to prevent any mis-adjustment resulting from shock or vibration.

FIGURES 3a and 3b illustrate the elfect that such relative movement of the modified I-shaped portion and the modified E-shaped portion 12 has on the air gap between the projection 14 and the center leg 20. In FIG- URES 3a and 3b, the windings and the end clamps have been removed to provide a clearer illustration. FIGURE 3a shows the relative positions of the portions 10, 12 for a maximum air gap (and hence greatest leakage) between the facing surfaces of the projection 14 and the center leg 20. In FIGURE 3a, it will be seen that the modified I-shaped portion 10 is at its extreme left position so that the left hand ends of the portions 10, 12 are aligned. FIGURE 3b, shows the relative positions of the portions 10, 12 for a minimum air gap (and hence smallest leakage) between the facing surfaces of the projection 14 and the center leg 20. In FIGURE 3b, the modified I-shaped portion is at its extreme right position so that the right hand ends of the portions 10, 12 are aligned. It will be appreciated that between the extreme left and right positions of FIGURES 3a and 3b, there are a number of intermediate positions which provide an almost infinite number of air gap spacings between facing surfaces of the projection 14 and the center leg 20.

In addition to providing an almost infinite number of adjustable air gap spacings, the invention permits this adjustment to be made after the transformer is assembled with its windings energized. The primary winding can be energized and the secondary winding can be loaded with any magnitude of resistance and the secondary current measured with an ammeter. With the transformer so connected and energized, it may be adjusted by relative movement of the modified I-shaped portion 10 and the modified E-shaped portion 12 until the secondary current has the desired magnitude for the desired load condition. Thus, the invention provides an improved arrangement that permits transformers to be mass-produced because relatively large variations in the dimensions of the portions 10, 12 may be compensated by adjustment of the portions 10', 12 after assembly.

While a number of embodiments of the invention have been built and constructed, one embodiment will be described in detail. This embodiment was a constant current, voltage step-up transformer that produced an output of secondary voltage between 4,000 and 6,000 volts with an input of 115 volts, 60* cycles applied to its primary winding. The transformer comprised 27 laminations, each being 0.025 inch thick. Each of the modified E-shaped laminations was 3.9 inches long and 1.4 inches wide. Each of the three legs was 0.7 inch wide. The primary winding space was 0.6 inch wide and the secondary winding space was 1.2 inches wide. The primary and secondary winding spaces each had a depth of approximately 0.7 inch. Each of the modified I-shaped laminations was approximately 3.8 inches long and 0.7 inch wide. The projection was approximately 0.8 inch wide and projected out approximately 0.1 inch. This provided a facing surface that sloped at an angle of approximately 7.5 degrees. The center leg of the E-shaped portion sloped at the same angle. The primary winding comprised approximately 830 turns of 0.010 inch diameter wire, and the secondary Winding comprised approximately 30,000 turns of 0.0028 inch diameter wire.

FIGURE 4 shows a curve that illustrates the ease with which the transformer just described (or any transformer in accordance with the invention) can be adjusted to provide the constant current. FIGURE 4 shows the secondary voltage plotted against the secondary current with the primary winding energized by 115 volts, 60 cycles, and with a suitable capacitor coupled across the secondary winding. Under open circuit conditions, the secondary voltage was approximately 9,000 volts (9 kv.). As increasing load (i.e., a decreasing resistance) was applied to the secondary winding, the secondary voltage decreased as indicated by the downwardly sloping solid line of FIGURE 4. For the transformer described above, the

downwardly sloping line approached a knee at a secondary current of about 8 milliamperes. When the secondary winding was short circuited, the secondary winding short circuit current was approximately 9.2 milliamperes. If the air gap between the facing surfaces of the projection of the I-shaped portion and the center leg of the E-shaped portion was correct, the secondary current remained constant as indicated by the substantially vertical, solid line portion of the curve. This con dition was obtained by adjusting the air gap by relative movement of the modified I-shaped portion and the IIlOdl fied E-shaped portion as previously described. Proper adjustment is indicated by the solid line curve labeled correct air gap. If the air gap was too small, the secondary current decreased as indicated by the dashed line curve labeled smaller air gap. If the air gap was too large, the secondary current increased as indicated by the dashed curve labeled larger air gap. Previous transformers usually had to be coarsely adjusted to one of several conditions represented by the addition or re moval of one or more shunt laminations. And, such ad dition or removal usually jarred or moved the shunt so that different results were obtained. However, because of the novel and improved vernier adjustment prov ed by the adjustable shunt core of the invention, the de sired and correct air gap is easily obtained. With the embodiment just discussed, the secondary current was constant for load voltages in the range between 4,000 and 6,000 volts.

It will thus be seen that the adjustable shunt core of the invention provides an improved leakage or high reactance transformer. Although the adjustable shunt core of the invention has been shown and described in connection with only one embodiment, the adjustable shunt core may have other embodiments. For example, the core may be formed of a modified I-shaped portion and a modified E-shaped portion, each of which is formed of a solid piece of magnetic material rather than being formed of a stack of laminations. The pro ection on the modified I-shaped portion may extend farther from the longitudinal part, with a correspond ng decrease in the length of the center leg of the modified E-shaped portion so as to provide the air gap nearer a point midway between the two portions. The slope angle of the facing surfaces may be varied with a relatively small angle pro viding a relatively fine adjustment and with a relatively large angle providing a relatively coarse ad ustment. And, of course, various transformers having various operating characteristics and ranges may be provided in accordance with the invention. However, all of such modifications and embodiments will be apparent to persons skilled 111 the art. Therefore, it is to be understood that modifications may be made without departing from the spirit of the invention or from the scope of the claim.

What I claim as new and desire to secure by Letters Patent of the United States is:

A transformer structure comprising: an E-shaped portion having a longitudinal member of a predetermined length, first and second outer legs extending from said longitudinal member, and an inner leg extending from said longitudinal member, the free end of said inner leg having a surface that slopes at an angle relative to said longitudinal member; an I-shaped portion having a longitudinal member of a length slightly less than said predetermined length and a saw tooth portion extending from said longitudinal member, said saw tooth portion on said I-shaped portion having a surface that slopes at substantially said angle relative to said longitudinal member of said I-shaped portion; means for clamping said I- shaped portion to said E-shaped portion so that said longitudinal member of said I-shaped portion engages the ends of said outer legs of said E-shaped portion d forms substantially coplanar butt joints therewith d so that said saw tooth portion on said I-shaped portion and said inner 011 d E-shaped portion have facing surfaces that are substantially parallel to each other and that are spaced at distance determined by the relative longitudinal position of said I-shaped portion and said E- shaped portion; said clamping means engaging the ends of the I-shaped portion and E-shaped portion, said clamping means thereby continuously exerting a clamping force on both said I-shaped portion and said E-shaped portion while one of said portions is moved relative to the other, and a notch in one of said portions for engaging a tool for moving said one portion relative to said other portion.

References Cited by the Examiner UNITED STATES PATENTS 1,874,806 8/1932 Ross 336-133 2,343,101 2/1944 Vogt 336-l34 X 3,127,581 3/1964 Rasmussen 336--2 10 X LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, C. TORRES, Assistant Examiners. 

